Sometimes generically called "hidden lilies" because these tropical herbaceous plants go dormant during the winter dry season, curcuma actually refers to any of about 40 species of tropical plants. Members of the ginger family, Zingiberaceae, the flowers appear hidden among the leaves and stems during the rainy summer season.
All 40 species of curcuma hail from the seasonally wet-to-dry forests of Southeast Asia, India and Malaysia. A few species grow in extreme northern Australia and southernmost China, too.
Some curcuma species grown commonly in tropical gardens bear catchy names. Siam tulip (Curcuma alismatifolia), jewel-of-Thailand (Curcuma petiolata), emerald pagoda (Curcuma harmandii), red fireball (Curcuma flaviflora) and striped curcuma (Curcuma rabdota) grow naturally across Thailand. In India, native plants include the zedoary (Curcuma zedoaria) and the giant plume (Curcuma elata). Indonesian species include Sumatra hidden lily (Curcuma sumatrana) while the jewel-of-Burma (Curcuma roscoeana) grows naturally across India, Southeast Asia and Malaysia, not just in Burma.
In spring when moisture returns, the leaves emerge from the soil like green needles. Each unfurls to reveal a large oval green leaf with pleated veins and often a central midrib blushed in red or dark burgundy. Then, in summer's heat and abundant rains, flower stalks emerge from the ground and reveal a rounded or cylindrical bract that rises above the leaves or remains nestled and hidden just under the foliage among the stems. These bracts are waxy modified leaves ranging in colour from red and pink to pale green, white or peach. Small yellow flowers emerge from the cluster of bracts. The foliage naturally dies away in autumn when the summer rains diminish, leaving a bare patch of ground.
Grow curcuma plants in frost-free conditions outdoors in a sand-based soil containing lots of organic matter. Generally speaking, that means grow them outdoors year-round in USDA hardiness zones 9 or 10 and warmer. In winter, do not water and allow only natural rainfall to moisten the soil. As long as the rhizome roots remain dormant and protected underground, light frosts can occur without harm. In spring, when hints of the first leaves emerge, increase watering to 1 inch per week, even more so in the heat of summer when plants are actively growing and flowering. Fertilise freely at this time, too. Once leaves naturally wane and die back in early autumn, reduce watering until all foliage disappears by winter's start, when no irrigation must occur. In cold climates, many curcuma grow well in containers as houseplants, or brought indoors over winter and then relocated outside once danger of frosts ends.
In tropical climes, curcuma provide seasonal interest in foliage and flowers in a mixed shrub border. They grow well as houseplants, even though they naturally die back and go into dormancy every winter. The flower stalks and colourful bracts provide an exotic, long-lasting source for cut flowers in bouquets and arrangements. Leaves with pronounced red-coloured midveins become decorative filler in these arrangements as well.
The dried powder from ground rhizomes of the species Curcuma longa provides the spice turmeric.